Screenshot of individual Xinerama heads

Xinerama-based multi-head setups have only one virtual screen. If the physical screens are different in height, you will find dead space in the screenshot. In this case, you may want to take screenshot of each physical screen individually. As long as Xinerama information is available from the X server, the following will work:

Screenshot of the active/focused window

The following script takes a screenshot of the currently focused window. It works with EWMH/NetWM compatible X Window Managers. To avoid overwriting previous screenshots, the current date is used as the filename.

scrot

scrot, which is available in the official repositories, enables taking screenshots from the CLI and offers features such as a user-definable time delay. Unless instructed otherwise, it saves the file in the current working directory.

scrot -t 20 -d 5

The above command saves a dated .png file, along with a thumbnail (20% of original), for Web posting. It provides a 5 second delay before capturing in this instance.

You can also use standard date and time formatting when saving to a file. e.g.,

scrot ~/screenshots/%Y-%m-%d-%T-screenshot.png

saves the screenshot in a filename with the current year, month, date, hours, minutes, and seconds to a folder in your home directory called "screenshots"

GNOME

Note: If <Prt Scr> complains about not finding gnome-screenshot or there is no "Take Screenshot" entry in your menu, you will need to install the gnome-utils package from [extra].

Other Desktop Environments or Window Managers

For other desktop environments such as LXDE or window managers such as Openbox and Compiz, one can add the above commands to the hotkey to take the screenshot. For example,

import -window root ~/Pictures/`date '+%Y%m%d-%H%M%S'`.png

Adding the above command to the <Prt Scr> key to Compiz allows to take the screenshot to the Pictures folder according to date and time.
Notice that the rc.xml file in Openbox does not understand commas; so, in order to bind that command to the <Prt Scr> key in Openbox, you need to add the following to the keyboard section of your rc.xml file:

Virtual console

If you merely want to capture the text in the console and not an actual image, you can use setterm, which is part of the util-linux package. The following command will dump the textual contents of virtual console 1 to a file screen.dump in the current directory:

sudo setterm -dump 1 -file screen.dump

Root permission is needed because the contents of /dev/vcs1 need to be read.